Taken together, the test and its administration is an industry unto itself, worth around $20 million a year.

It's a little troubling, given that Myers and Briggs were a mother (Katharine Briggs) and daughter (Isabel Myers) who studied the works of psychologist Carl Jung a hundred years ago, particularly his book "Psychological Types." Myers and Briggs weren't social scientists themselves. Briggs was a housewife with a deep interest in Jung; before she wrote a survey that served as a prototype of Myers-Briggs personality tests, Myers wrote mystery novels.

... Jung didn't believe that types were easily identifiable, and he didn't believe that people could be permanently slotted into one category or another. "Every individual is an exception to the rule," he wrote; to "stick labels on people at first sight," in his view, was "nothing but a childish parlor game."

Cambridge University professor Brian Little says another main reason for the test's ongoing success is that it's been "marketed brilliantly." But, of course, "you have to have something of merit in order to market well."

The merits are there: Little says that the test gives people the chance to discuss their preferences and personality in the workplace — a conversation that otherwise gets crowded out.

This makes people available to insight into themselves. When taking a personality test (or looking into a horoscope), you get the feeling of a-ha! Yes, I am an introvert, so please don't bother me. And that's satisfying.

As well, the test is decidedly positive. Unlike other psych measurements, the Myers-Briggs doesn't separate people into adaptive or maladaptive, functioning or dysfunctional, stable or neurotic.

Yet identifying that you're a particular "type" of person — introvert or extrovert, for example — is both a strength and a weakness, Little says.

The strength is that people find it fascinating. The weakness is that it's limiting.

Once people find out their type, they take it as a "badge that they stamp on their forehead and use as an identity marker," Little says. In extreme cases, people get tattoos.

This is a problem.

"If you only see yourself as an extrovert or as one of those four-letter codes on the Myers-Briggs," Little says, "you will have foreclosed on paths that might open to you if didn't think in terms of types of people."

Other critics of the Myers-Briggs test are more forceful.

• Wharton organizational psychologist Adam Grant criticizes the either/or approach of the system. Thirty years of research show that you can both be a thinker and a feeler; in fact most thoughtful people also spend lots of time feeling emotion. "When I scored as a thinker one time and a feeler one time, it's because I like both thinking and feeling," he writes. "I should have separate scores for the two."

• Philosopher Roman Krznaricnotes that if "you retake the test after only a five-week gap, there's around a 50% chance that you will fall into a different personality category compared to the first time you took the test." This is bad news for the test's reputation, given that replicability is an essential part of scientific inquiry.

• In a review of research comparing Myers-Briggs personality types and job performance, management scholars William Gardner and Mark Martinko find that "few consistent relationships between type and managerial effectiveness have been found."

The best alternative to the Myers-Briggs is the "Big 5" personality types, which operate along five continuums: conscientiousness, agreeability, emotional stability, openness to experience, and extroversion. As well, the Big 5 traits have been observed by social scientists and tested in the lab and in the field.

For the record, the Myers-Test doeshave supporting studies, but as Paul writes in "The Cult Of Personality Testing," the research lies outside the lines of psycholigical science:

"Myers-Briggs proponents like to point to the more than 7,800 studies that they say have been conducted on the MBTI. But a significant number of these articles were published in specialty publications like "The Journal of Psycholigical Type," "MBTI News," and "TypeWorks." Many others appear in books produced by CPP, the Indicator's distributor. And most research on the Myers-Briggs is concerned with exploring applications for the test — not with proving or refuting its basic legitimacy."

When people pursue their personal projects, they're able to act in ways that fall outside the prescriptions of their "type." The extrovert acts like an introvert to study for the LSAT; the curmudgeonly manager acts like an angel to impress his wife's parents.

"We're not helping ourselves when we pin ourselves into categories that will limit us," Little says. "I prefer to not to look at the traits we have but the deeds we do, the projects we pursue, as more of a fruitful inroad into human personality."